@heme725
Here is my personal experience.
1) I was able to get my aim on target fast, but staying on target was quite difficult. Recoil, muzzle flash, opponent crouching and/ or moving suddenly.
Most of those things I don't have to worry about when using my controller at all. Basically I had to mentally be focused while using a mouse & keyboard as every step of the way matters, there is no downtime. On the controller I could be mentally distracted most of the match, but still be fine ingame.
2) Close range was odd on the mouse & keyboard as the tracking changed so suddenly. On a controller it's super easy to follow, but mouse & keyboard is another thing.
3) Another issue is the keyboard, I dislike it. It's super hard for me coming from years of controller to the input device to be honest. Using 4 keys over an analog stick is tough, I missed it every step of the way.